Phytolith transport in soil: A field study using fluorescent labelling

Soil phytoliths have been widely applied to reconstruct vegetational history. To date, however, the transport behaviour of phytoliths in soil is poorly understood, causing uncertainties in the interpretation of phytolith data. The present study was therefore designed: (1) to determine transport rates of phytoliths in loamy and sandy soils under field conditions and (2) to elucidate the effect of phytolith size and shape on their transport behaviour in sandy and loamy soils. For this purpose, we adopted a fluorescent labelling technique from veterinary science. The phytoliths were extracted from common reed (Phragmites australis), labelled with the fluorescent dye fluorescein isothiocyanate, and applied to a loamy sand soil (Haplic Cambisol) and a silty loam soil (Stagnic Luvisol) in southern Germany. One year after application, the soils were sampled to analyse phytolith distribution with soil depth. The weighted mean transport distance of phytoliths after one year was 3.99 ± 1.21 cm for the Cambisol and 3.86 ± 0.56 cm for the Luvisol. Phytolith size significantly affected transport behaviour, indicating a preferential translocation of small-sized phytoliths. Our study provides direct evidence for a significant downward mobility of phytoliths in sandy and loamy soils under natural conditions. This should be taken into account when using phytoliths as palaeoenvironmental tracers. Quantifying phytoliths in soil with fluorescent labelling makes it possible to identify artificially applied phytoliths without using the conventional extraction method.